For example, when an automobile bumper made of a resin is painted with a paint of a vehicle color, an air intake port of the bumper is masked for preventing an application of the paint thereto, and then the bumper is painted. Thus, the masked part remains to be unpainted.
As an example of such a masking method, a use of a synthetic resin sheet formed by molding a thermoplastic resin or the like into a predetermined shape has been known (see, JP8-24773A, for example). The synthetic resin sheet is previously molded into a shape conformed to a predetermined part (part to be masked) of a surface to be unpainted, by a vacuum molding, press molding, blow molding, and so on.
Since the conventional masking material for painting is easily fixed on a part to be masked, a time required for the masking operation is short enough.